1. Field of the Invention
The present invention relates to optical disk drives which can read and write optical disks. More specifically, the present invention provides a multi-beam optical system for simultaneously writing multiple tracks of an optical disk.
2. Background of the Invention
Current writable optical disk technologies include several write-once technologies, such as CD-Recordable (CD-R) and DVD-Recordable (DVD-R), as well as re-writeable technologies, such as CD-Re-writeable (CD-RW), DVD Re-writeable (DVD-RW), and DVD-RAM.
Data is typically recorded on writeable optical disks by using a writing beam having a higher power than is used for reading. The media for use with optical disk writers typically includes a recording layer, made of a material which changes its optical characteristics in response to the presence of the beam from the high power laser. The high power laser is used to create “pits” in the recording layer which have a different reflectivity than surrounding areas of the disk, and which can be read using a lower power reading beam.
Because in most previously known optical disk systems the data are read from or written to the disk serially, i.e., one bit at a time, the maximum data transfer rate for an optical disk reader is determined by the rate at which the pits pass by the pickup assembly. Because the linear density of the bits and the track pitch are fixed by the specification of the particular optical disk format, the data transfer rate of optical disk readers is limited by the rotational speed of the disk itself. However, high disk rotational speeds place increased demands on the optical and mechanical subsystems within the optical disk player, create greater vibration, and may make such players more difficult and expensive to design and manufacture.
Furthermore, in recording systems, the minimum energy required to form a mark of a given length is determined by the chemical and thermal properties of the recording disk medium. The laser energy impinging on the mark area is proportional to laser power and inversely proportional to disk rotational speed. Thus, for a given laser power, there is a practical upper limit to the disk rotational speed during recording.
A cost effective alternative to increasing the disk rotational speed to provide faster optical disk drives is to read or write multiple data tracks simultaneously, as described in commonly assigned U.S. Pat. No. 5,426,623 to Alon et al. In accordance with the methods and apparatus provided therein, for example, ten adjacent data tracks may be read simultaneously. Thus, even if the disk is rotated at only 8× the standard speed, the capability to read ten tracks simultaneously provides the equivalent of an 80× drive.
It would therefore be desirable to provide an optical drive that achieves improved writing speeds by writing data to multiple tracks of an optical disk simultaneously.